Owing to their very low internal capacitance, present-day power semiconductor devices have an extremely high switching speed. This high switching speed is not always an advantage. Compensation devices, in particular, switch noticeably faster and more steeply than conventional MOSFET devices. In non-optimised applications, however, the very steep di/dt may in a shut-down process on parasitic inductances of the application circuit generate very high voltage peaks, which can destroy the semiconductor device. There is further a risk that vibrations may be caused in the shut-down process by the steep di/dt, which would affect the EMC (electromagnetic compatibility).
The di/dt can be limited by a larger switching resistor, which, however, slows down the overall switching process as an additional component. As a result, the advantage of fast switching and the reduced switching losses associated therewith can be lost completely or even reversed by the series-connected switching resistor, as the time constant resulting from the internal switching resistor and the internal capacitance between a control electrode of the semiconductor device and an output electrode is on the one hand increased by the series-connected additional switching resistor, thus attenuating or slowing down the switching process, while on the other hand switching losses increase noticeably as a result of the additional ohmic resistance.